Picture display device and method of driving the same

ABSTRACT

In a picture display device, a picture having high gradation is obtained by using an alternating method which can deal with a video signal having a high frequency band region. On the basis of an input signal, a signal processing circuit outputs a pair of analog video signals (a signal reversal frequency is one frame), which have inversion relationships with each other, to a signal line drive circuit, and the signal line drive circuit applies one of the inputted pair of video signals to an odd signal line, and applies the other of the video signals to an even signal line, so that source line reversal drive is carried out.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a driving method suitable for an activematrix type display which uses a display medium such as a liquid crystaland has a built-in driving circuit, and particularly to an alternatingdrive method of a liquid crystal panel.

2. Description of the Related Art

FIG. 7 is a block diagram of a conventional liquid crystal displaydevice.

A liquid crystal panel 1 includes a plurality of scanning lines 2extending in parallel with each other in the horizontal direction, aplurality of signal lines 3 extending in parallel with each other in thevertical direction intersecting the scanning lines at right angles, TFTs(thin film transistors) disposed near the intersecting portions of thescanning lines and the signal lines, and pixel electrodes connected tothe TFTs. One end of each of the scanning lines 2 is connected to a gateelectrode of each of the TFTs and the other end thereof is connected toa gate driver circuit 4 (scanning line drive circuit). One end of eachof the signal lines 3 is connected to a source electrode of each of theTFTs and the other end thereof is connected to a source driver circuit 5(signal line drive circuit).

A video signal from a signal processing circuit 6, and a start pulsesignal, a clock signal, a horizontal synchronizing signal, etc. from acontrol circuit 7 are inputted to the source driver circuit 5.

The signal processing circuit 6 includes an analog/digital (A/D)conversion circuit 14, a correcting circuit 8, a digital/analog (D/A)conversion circuit 9, a reversal process circuit 10, and the like.

The control circuit 7 is a circuit for forming, on the basis of a videosignal, pulses (start pulse, clock pulse, synchronizing signal, polarityreversal signal, etc.) necessary for the gate driver circuit 4, thesource driver circuit 5, the signal processing circuit 6, and the likeand for outputting the pulses.

The operation of the conventional liquid crystal display devicestructured as described above will be described.

First, while using an inputted synchronizing signal as a reference, thecontrol circuit 7 repeats an operation (frequency division) of countinga predetermined count number (frequency division ratio) of clocks, withan oscillation clock signal (OSC) outputted from a phase synchronizedoscillator as a basic oscillation. The control circuit 7 counts theclocks at the same time as the frequency division, and forms a startpulse 23 (SPD) in the screen horizontal direction, a start pulse 24(SPS) in the screen vertical direction, a clock pulse 25 (CLD) in thescreen horizontal direction, a clock pulse 26 (CLS) in the screenvertical direction, and a polarity reversal signal 22 (FRP). There isalso a case where a horizontal synchronizing signal (HYS) and a verticalsynchronizing signal (VSY) are formed. In this case, the HSY and the VSYare used as references in the horizontal and vertical directions when,for example, characters are displayed on the screen.

An input video signal 20 includes such signals that picture signals ofone screen (frame) are divided by the number of lines in thelongitudinal direction (vertical direction), and the signals the numberof which is equal to the number of lines in the longitudinal directionare continuous. Data in one pixel unit, that is, respective data of red(R), green (G), and blue (B) are made one set and are transmitted everyunit time to an input video signal line.

Correspondingly to the input video signal 20, in a pixel region 11,pixels of R, G, and B corresponding to different three colors of red,green, and blue are sequentially repeatedly arranged in the lateraldirection (horizontal direction) of the panel to make up a pixel row,and a pixel column is made up in the longitudinal direction (verticaldirection). For example, if the pixel region 11 is made up of 640 pixelsin the horizontal and 400 pixels in the vertical, a video signal of onescreen includes such signals that lines in the horizontal direction,each including information signals of 640 pixels in the horizontal, arecontinuous by the number (400 columns) of lines in the verticaldirection. In general, the input video signal is a signal correspondingto a CRT, and is not a signal suitable for liquid crystal panel display,so that it is necessary to carry out various signal processes.

In the signal processing circuit 6, a γ correcting process in view ofliquid crystal characteristics, an analog/digital signal (A/D)converting process, a digital/analog signal (D/A) converting process, analternating process to improve the reliability of liquid crystal, andthe like are performed to the input video signal from an externaldevice.

In this signal processing circuit 6, for the purpose of obtainingexcellent display, various corrections are carried out to the inputvideo signal inputted from the outside. For the corrections, analog RGBsignals are first converted into digital RGB signals by theanalog/digital signal (A/D) conversion circuit 14. The γ correctingprocess in view of the liquid crystal characteristics and the like areperformed to the video signal converted into digital signals andcorrections are made. The corrected video signals are again convertedinto analog RGB signals by the digital/analog signal (D/A) conversioncircuit 9.

Next, by the reversal process circuit 10, the video signals aresubjected to the alternating process and the like to improve thereliability of liquid crystal. A polarity reversal signal 22 (FRP) as asignal to determine the timing for carrying out polarity reversalnecessary for driving the liquid crystal panel is inputted to thereversal process circuit 10 from the control circuit 7. The reversalprocess circuit 10 is a circuit for inverting the video signal inaccordance with the polarity reversal signal 22 (FRP).

In this way, the signal processing circuit 6 processes the input videosignal 20 into an analog video signal 27 suitable for display of theliquid crystal panel. This video signal (subjected to the γ correction,alternating process, and the like) is inputted to the liquid crystalpanel 1.

Next, this video signal 27, the SPD 23 formed in the control circuit 7,and the CLD 25 are inputted to the source driver circuit 5 provided inthe liquid crystal panel 1. The SPD 23 is a signal regulating the timingin one horizontal period when display is started. The CLD 25 is a signalcorresponding to the respective pixels in the horizontal direction, andin accordance with this signal, the source driver circuit samples thevideo signal from the signal processing circuit and outputs a voltage(video signal) corresponding to the respective pixels to the signal line3. FIG. 9 is a timing chart in the source driver circuit.

The SPS 24 and the CLS 26 formed in the control circuit 7 are inputtedto the gate driver circuit 4. The SPS 24 is a signal regulating thetiming in one vertical period when display is started. The CLS 26 is asignal corresponding to the respective pixels in the vertical direction,and it is designed such that in accordance with this signal, scanning iscarried out every one horizontal period from the upper portion of thescreen and the screen is displayed.

The design of displaying the screen will be described in detail withreference to FIGS. 8A and 8B.

First, in accordance with a signal from a shift register, with respectto the signal line (1), only one portion (pixel A1) of a lateraldirection (horizontal direction) line of the video signal 27 is selectedand sampled, and its potential is applied to the entire of the signalline (1). A signal voltage (turning on a TFT provided in the vicinity ofan intersecting portion) is applied to only a scanning line A. Then,only the TFT provided in the vicinity of the intersecting portion of thesignal line (1) and the scanning line A is turned on and the potentialof the signal line (1) is applied to the pixel A1. In this way, part ofpicture image information is written in the pixel A1.

Next, while the state where the pixel A1 has been written is held byauxiliary capacitance or the like, at a next instance, only one portion(pixel A2) in the lateral direction (horizontal direction) line of thevideo signal is selected and sampled, and its potential is applied to asignal line (2) adjacent to the signal line (1). In this way, part ofthe picture image information is written also in the pixel A2 similarlyto the pixel A1. This process is sequentially repeated, so that part ofthe picture image information is sequentially written in the first pixelline (A row) in the lateral direction. During this, the signal turningon the TFT provided in the vicinity of the intersecting portion isapplied to the scanning line A.

After writing in all of the first pixel row A in the lateral directionis ended, a signal voltage (turning on a TFT provided in the vicinity ofan intersecting portion) is next applied to only a scanning line B. Inthe signal line (1), only one portion (pixel B1) of the video signal issampled, and its potential is held. Similarly to the above, only pixelrow (B row) corresponding to the second row in the lateral direction issequentially written. Such operations are repeated n times, n being thenumber of pixel rows (n rows), so that one screen is displayed.

In general, in a liquid crystal display using TFTs, for the purpose ofpreventing deterioration of a liquid crystal material, eliminatingdisplay blur, and keeping display quality, voltages that the polaritiesof which are inverted every one frame or predetermined period areapplied (alternated) to the respective pixels.

One of conventional typical alternating drive methods in a liquidcrystal display panel will be described with reference to FIGS. 10 andFIG. 11. Here, for simplification, an example is shown while using amodel screen (FIG. 11A) of display pixels of 6 rows ×6 columns as partof a display region.

First, the polarity reversal signal 22 (FRP) for inverting the polarityof the input video signal 20 is formed by the control circuit. Thewaveform of this polarity reversal signal 22 is shown in FIG. 10. On thebasis of such polarity reversal signal (FRP), the polarity of the videosignal is inverted. This video signal has a signal waveform in which thepolarity is inverted from the positive to the negative or from thenegative to the positive every one pixel.

Thus, the panel display as shown in FIG. 11B is obtained. The videosignals having the same polarity (positive or negative) are applied tothe pixel electrodes denoted by A1, B1, C1, . . . , A3, B3, C3, . . . ,and A5, B5, C5, . . . . Similarly, although the video signals having thesame polarity (negative or positive) are applied to the pixel electrodesdenoted by A2, B2, C2, . . . , A4, B4, C4, . . . , and A6, B6, C6, . . ., the polarity is opposite to the pixel electrode A1. That is, the videosignals having opposite polarities between adjacent pixels in thelateral (horizontal) direction are applied to the respective pixels.Besides, as shown in FIG. 11C, in the next screen (frame), the videosignals having polarities opposite to the previous screen (frame) areapplied to the respective pixels. By repeating this operation,alternating drive is carried out. Such an alternating method is called asource line inversion (or reversal), or a column inrevrsion.

As other alternating drive methods of display of a liquid crystaldisplay panel, as shown in a display pattern view of FIG. 12A, there isproposed an alternating ethod (frame reversal method) in which thepolarity of a video signal is inverted at each time when one screen(frame) is written and the video signal is applied to the pixels.

However, in this method, a polarity reversal period is as long as oneframe, and becomes a frequency region (about 30 Hz) which can berecognized by human eyes, so that an observer recognizes a subtledifference between the display where the polarity of the video signal ispositive and the display where the polarity of the video signal isnegative, as a flicker.

Moreover, as another alternating drive method to lower the flickerproduced by the above frame reversal method, as shown in a displaypattern view of FIG. 12B, there is proposed an alternating method (gateline reversal method) in which the polarity of a video signal isinverted every writing of adjacent one scanning line and the videosignal is applied to the pixel. In this method, the video signals havingopposite polarities between adjacent pixels in the longitudinal(vertical) direction are applied to the respective pixels. In thismethod, the polarity of the video signal is inverted from the positiveto the negative or from the negative to the positive every onehorizontal scanning period.

In addition, as an alternating drive method where it is hardest toproduce a flicker., as shown in a display pattern view of FIG. 12C,there is proposed an alternating method (dot reversal method) in whichthe polarity of a video signal is inverted at each time of writing ofadjacent all pixels and the video signal is applied to the pixel. Inthis method, a video signal having a polarity opposite to adjacentpixels in the lateral (horizontal) direction and the longitudinal(vertical) direction is applied to the respective pixels. Also in thismethod, like the source line reversal, the polarity of the video signalis inverted from the positive to the negative or from the negative tothe positive every one pixel. However, this alternating drive method cannot be applied to all cases, and it has been impossible to carry outthis method in interlace drive which is the main current at present, forexample, in a two-line simultaneous writing method.

Like this, in the conventional alternating methods, as shown in FIG. 10,in order to invert the polarity of a video signal every one pixel or onehorizontal period from the positive to the negative or from the negativeto the positive, it is necessary to newly charge the capacitance of thevideo signal line every one pixel or every one horizontal scanningperiod, so that its consumed electric power is large.

Moreover, in the conventional structure, there are problems that if thepolarity reversal period of the video signal is long, lowering (colorshift, flicker, etc.) of display characteristics occurs, and if thepolarity reversal period of the video signal is short, a phase shift, anoise, dulling of a signal waveform, and the like occur and inaccuratealternating drive is caused.

The number of display pixels of a display increases year-by-year, and ina panel having a high number of pixels, a drive frequency becomes veryhigh. For example, in the NTSC standard, it is necessary that the numberof pixels is about 400 thousands, and in the HDTV standard, it isnecessary that the number of pixels is about 2 millions. Thus, themaximum frequency of an inputted video signal is about 6 MHz for theNTSC standard, and about 20 MHz to 30 MHz for the HDTV standard. Inorder to accurately display this video signal, it is necessary that theclock signal has a frequency (for example, about 50 MHz to 60 MHz)several times the video signal. In future, it is expected that fine andhigh quality display is still more required, and a video signal having avery fast dot clock comes to be processed.

Conventionally, it has been difficult to drive a liquid crystal panelwhile accurately alternating a video signal and a clock signal havingsuch a high frequency band region. And also, it has been very difficultto constitute a circuit operating at a high frequency band region byTFTs using, for example, amorphous silicon or polycrystalline silicon.

SUMMARY OF THE INVENTION

The present invention has been made to overcome the foregoing problems.

An object of the present invention is therefore to provide excellentdisplay by using an alternating method which can deal with an inputvideo signal with a relatively high picture quality, and further toprovide a liquid crystal display device in which consumed electric poweris decreased.

In order to achieve the object, according to a first aspect of thepresent invention, a method of driving a picture display device whichcomprises a liquid crystal panel including a switching element for eachof pixel electrodes, a scanning line drive circuit for driving scanninglines of the liquid crystal panel, a signal line drive circuit fordriving signal lines of the liquid crystal panel, a control circuit forcontrolling drive of the liquid crystal panel, and a signal processingcircuit, is characterized in that the signal processing circuit outputsa pair of video signals having a reversal relationship with each otherto the signal line drive circuit.

According to a second aspect of the present invention, a method ofdriving a picture display device which comprises a liquid crystal panelincluding a switching element for each of pixel electrodes, a scanningline drive circuit for driving scanning lines of the liquid crystalpanel, a signal line drive circuit for driving signal lines of theliquid crystal panel, a control circuit for controlling drive of theliquid crystal panel, and a signal processing circuit, is characterizedin that a pair of video signals having symmetry with reference to apotential of an opposite electrode provided opposite to the pixelelectrode is inputted to the signal line drive circuit.

According to a third aspect of the present invention, a method ofdriving a picture display device which comprises a liquid crystal panelincluding a switching element for each of pixel electrodes, a scanningline drive circuit for driving scanning lines of the liquid crystalpanel, a signal line drive circuit for driving signal lines of theliquid crystal panel, a control circuit for controlling drive of theliquid crystal panel, and a signal processing circuit, is characterizedin that the signal processing circuit outputs plural pairs of videosignals having reversal relationships with each other to the signal linedrive circuit.

According to a fourth aspect of the present invention, a method ofdriving a picture display device which comprises a liquid crystal panelincluding a switching element for each of pixel electrodes, a scanningline drive circuit for driving scanning lines of the liquid crystalpanel, a signal line drive circuit for driving signal lines of theliquid crystal panel, a control circuit for controlling drive of theliquid crystal panel, and a signal processing circuit, is characterizedin that plural pairs of video signals, each pair having symmetry withreference to a potential of an opposite electrode provided opposite tothe pixel electrode, is inputted to the signal line drive circuit.

According to a fifth aspect of the present invention, a method ofdriving a picture display device which comprises a liquid crystal panelincluding a switching element for each of pixel electrodes, a scanningline drive circuit for driving scanning lines of the liquid crystalpanel, a signal line drive circuit for driving signal lines of theliquid crystal panel, a control circuit for controlling drive of theliquid crystal panel, and a signal processing circuit, is characterizedin that the signal processing circuit outputs at least one first videosignal and at least one second video signal to the signal line drivecircuit, the first video signal is applied to an odd signal line of thesignal lines, the second video signal is applied to an even signal lineof the signal lines, polarities of signal potentials of the first videosignal and the second video signal are inverted every one horizontalperiod, and the first video signal has a reversal relationship with thesecond video signal.

In the above structure, the ethod of driving a picture display device ischaracterized in that the signal line drive circuit and the scanningline drive circuit make driving in a lateral direction while invertingpolarities of signal potentials of adjacent ones of the pixel electrodeswith reference to a potential of an opposite electrode provided oppositeto the pixel electrode, and further make driving while inverting apolarity of a signal potential of each of the pixel electrodes everyframe period.

According to a sixth aspect of the present invention, a method ofdriving a picture display device which comprises a liquid crystal panelincluding a switching element for each of pixel electrodes, a scanningline drive circuit for driving scanning lines of the liquid crystalpanel, a signal line drive circuit for driving signal lines of theliquid crystal panel, a control circuit for controlling drive of theliquid crystal panel, and a signal processing circuit, is characterizedin that the signal processing circuit outputs at least one first videosignal and at least one second video signal to the signal line drivecircuit, the first video signal is applied to an odd signal line of thesignal lines, the second video signal is applied to an even signal lineof the signal lines, polarities of signal potentials of the first videosignal and the second video signal are inverted every frame period, andthe first video signal has a reversal relationship with the second videosignal.

In the above structure, the method of driving a picture display deviceis characterized in that the signal line drive circuit and the scanningline drive circuit make driving in a lateral direction while invertingpolarities of signal potentials of adjacent ones of the pixel electrodeswith reference to a potential of an opposite electrode provided oppositeto the pixel electrode, invert a polarity of a signal potential everypixel in a vertical direction, and further make driving while invertinga polarity of a signal potential of each of the pixel electrodes everyframe period.

In the picture display device of each of the respective structures setforth above, liquid crystal is filled between two transparent insulatingsubstrates, a plurality of scanning lines arranged in parallel on theinner surface of one of the substrates and a plurality of signal linesarranged in parallel are formed so as to intersect each other, pixelelectrodes are formed in regions surrounded by the scanning lines andthe signal lines, thin film transistors (TFT) are formed near theintersecting portions of the scanning lines and the signal lines, and anopposite electrode is formed on the inner surface of another substrates.

According to another aspect of the present invention, a picture displaydevice is characterized in that the device is driven by any one of themethods of driving the picture display device set forth above.

According to a seventh aspect of the present invention, a picturedisplay device comprises a liquid crystal panel including a switchingelement for each of pixel electrodes, a scanning line drive circuit fordriving scanning lines of the liquid crystal panel, a signal line drivecircuit for driving signal lines of the liquid crystal panel, a controlcircuit for controlling drive of the liquid crystal panel, and a signalprocessing circuit, and is characterized in that the signal processingcircuit is connected to the liquid crystal panel through a plurality ofvideo signal lines, and includes D/A conversion circuits connected tothe plurality of video signal lines, the number of D/A conversioncircuits being equal to the number of video signal lines.

The picture display device is particularly suitable for a projectiontype display means including a transmission type liquid crystal paneland a light source for projection.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a block diagram showing an embodiment of the presentinvention;

FIG. 2A is a partial circuit diagram of the periphery of a source drivercircuit shown in FIG. 1, and FIG. 2B is a view showing a displaypattern;

FIG. 3 is a timing chart of each of signals in a source driver circuitshown in FIG. 2;

FIG. 4 is a view showing signal voltage waveforms showing an embodimentof the present invention;

FIG. 5A is a partial circuit diagram of the periphery of a source drivercircuit shown in embodiment 3, and FIG. 5B is a view showing a displaypattern;

FIG. 6 is a view showing a schematic structure of a rear projectorrelating to the present invention;

FIG. 7 is a block diagram showing a conventional liquid crystal displaydevice;

FIG. 8A is a partial circuit diagram of the periphery of a source drivercircuit shown in FIG. 7, and FIG. 8B is a view showing a displaypattern;

FIG. 9 is a timing chart of each of signals in a source driver circuitshown in FIG. 8;

FIG. 10 is a view showing signal voltage waveforms of a conventionalmethod;

FIGS. 11A to 11C are views showing polarities of respective pixels insource line reversal drive;

FIGS. 12A to 12C are views showing polarities of respective pixels invarious reversal drive methods; and

FIG. 13 is a block diagram showing an applied example of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

Preferred embodiments of the present invention will be described below.The present invention is not limited to the embodiments.

EMBODIMENT 1

FIG. 1 is a block diagram showing embodiment 1 of a liquid crystaldisplay device of the present invention. FIG. 1 shows a liquid crystaldisplay device mainly including a liquid crystal panel 101, a signalprocessing circuit 106, and a control circuit 107.

The signal processing circuit 106, the control circuit 107, and the likeare mounted on, for example, a different printed circuit, and areconnected to the liquid crystal panel 101 through a cable, a flexiblewiring plate, or the like. It is possible to form part or all ofperipheral circuits, such as the signal processing circuit 106 and thecontrol circuit 107, on a same substrate as an active matrix substrateof the liquid crystal panel 101 by using thin film transistors, whichmay be formed simultaneously as the active matrix circuits.

The liquid crystal panel 101 mainly includes a plurality of scanninglines 102 extending in parallel with each other in a horizontaldirection (lateral direction), a plurality of signal lines 103 extendingin parallel with each other in a vertical direction (longitudinaldirection) intersecting the scanning lines at right angles, TFTs (thinfilm transistors) disposed at the intersecting portions of the scanninglines and the signal lines, and pixel electrodes connected to the TFTs.

The TFT is used electrically as a switch, and is preferably formed byusing a silicon film or the like having crystallinity as a semiconductormaterial. In this embodiment, although a film obtained by using a quartzsubstrate and by means a crystallizing method (for example, techniquedisclosed in Japanese Patent Unexamined Publication No. Hei. 9-312260,or the like) using nickel as a catalytic element is used as the siliconfilm having crystallinity, the silicon film is not particularly limitedto this as long as the film has crystallinity and excellent mobility.Incidentally, Japanese Patent Unexamined Publication No. Hei. 9-312260discloses also a gettering technique to lower the concentration of thecatalytic element, and the present invention used the getteringtechnique as well. There is a pending U.S. patent application Ser. No.08/785,489, which corresponds to this Japanese patent. The entiredisclosure of these patents are incorporated herein by reference.

One end of each of the scanning lines 102 is connected to a gateelectrode of each of the TFTs, and the other end thereof is connected toa gate driver circuit 104. One end of each of the signal lines 103 isconnected to a source electrode of each of the TFTs and the other endthereof is connected to a source driver circuit 105.

In FIG. 1, although merely several signal lines 103 are shown, thenumber of signal lines are actually equal to the number of pixelelectrodes of the liquid crystal panel in the lateral direction.Similarly, the number of scanning lines 102 is equal to the number ofpixel electrodes of the liquid crystal panel in the longitudinaldirection.

The pixel electrode connected to the TFT together with a counterelectrode formed on the other substrate and liquid crystal constitute aliquid crystal capacitor. The counter electrode is connected to allliquid crystal capacitors, and has a common potential (centerpotential).

The control circuit 107 is a circuit for supplying, on the basis of aninput video signal, pulses (start pulse, clock pulse, synchronizingsignal, polarity reversal signal, etc.) necessary for the gate drivercircuit (scanning line drive circuit) 104, the source driver circuit(signal line drive circuit) 105, the signal processing circuit 106, andthe like.

In this embodiment, on the basis of an input video signal 120, a firstanalog video signal 129 and a second analog video signal 130 areoutputted by the signal processing circuit 106 to the source drivercircuit (signal line drive circuit) 105. FIG. 4 shows an example ofsignal waveforms of the input video signal 120, a video signal aftercorrection, a synchronizing signal 121, a polarity reversal signal 122,a first analog video signal 129, and a second analog video signal 130.In FIG. 4, for simplification, ends of the respective signals are notprovided. Besides, in the drawing, signals in second to n-th lines inone frame period are omitted.

The signal processing circuit 106 of this embodiment mainly includes ananalog/digital (A/D) conversion circuit 114, a correcting circuit 108,digital/analog (D/A) conversion circuits 109 and 110, reversal processcircuits 112 and 113, and the like. Although this embodiment uses theA/D conversion circuit 114 and the D/A conversion circuits 109 and 110each having a general structure, such a structure may be adopted thatthe circuits are made up of TFTs and are provided on the same substrateas the panel.

The A/D conversion 114 is used to convert the input video signal 120into a digital signal in which correction of a signal can be easilymade. In this embodiment, although an example in which an analog RGBsignal is used as the input video signal is shown, it is also possibleto use a digital RGB signal as the input video signal. In the case wherethe digital RGB signal is used as the input video signal, the A/Dconversion circuit 114 is not necessary for the structure of the presentinvention.

The correcting circuit 108 performs various corrections to the inputtedvideo signal (digital signal) by an arithmetic process and the like.This correcting circuit mainly carries out a y correction process andthe like to the video signal, and converts the video signal into asignal suitable for the liquid crystal panel display. In thisembodiment, processing of dividing the signal into two signals is alsocarried out in this correcting circuit. It is preferable that thiscorrecting circuit is made to have such a structure as includes astoring circuit for temporarily storing an inputted signal, a signaldelay circuit for correcting a phase shift caused by division of twosignals, and the like.

Two signals outputted from the correcting circuit 108 to differentsignal lines are respectively converted into analog signals by thecorresponding D/A conversion circuits 109 and 110. Here, in order toprevent a phase shift, signal lines (two), some D/A conversion circuits(two), and reversal process circuits (two) become necessary. However, ifthe caused phase shift is small and is within an allowable range, a D/Aconversion circuit (one) and a reversal process circuit (one) mayconstitute the signal processing circuit.

The reversal process circuits 112 and 113 are mainly made up ofamplifiers, amplify two signals to the intensity (−5 V to 5 V) suitablefor the liquid crystal panel, and invert the signals on the basis of thepolarity reversal signal 122 formed in the control circuit. In addition,the entire of either one of the signals is inverted, so that two signals(first analog video signal 129, second analog video signal 130) havingsymmetry are outputted.

The two signals obtained in this way are inputted to the source drivercircuit. As compared with a case where one signal is inputted to thesource driver circuit, it is also possible to reduce the operationfrequency to a half.

Two video signals from the signal processing circuit 106, the startpulse signal, clock signal, horizontal synchronizing signal, and thelike from the control circuit 107 are inputted into the source drivercircuit 105.

The source driver circuit 105 is made up of horizontal shift registersof two phases which can control scanning directions, and a samplingcircuit for sampling the picture signal to drive a pixel portion. Thesampling circuit is made up of a plurality of switching TFTs andcapacitors.

FIG. 2 is a circuit diagram showing the inner structure of the sourcedriver circuit in the embodiment 1. The source driver circuit shown inFIG. 2 can be made up of various circuits, typically of a shiftregister, a level shifter, a switch, an inverter, an output buffercircuit, and the like. The circuit is not limited to the structure ofthis embodiment as long as the circuit samples the picture signal andapplies it to a display portion.

In FIG. 2, although merely several signal lines are shown, the number ofsignal lines is actually equal to the number of pixel electrodes of theliquid crystal panel in the lateral direction. Similarly, the number ofscanning lines is equal to the number of pixel electrodes of the liquidcrystal panel in the longitudinal direction. FIG. 3 is a timing chart inthis source driver circuit.

The gate driver circuit in the vertical direction includes a verticalshift register which can make control in the scanning direction, a levelshifter for converting an output signal of the shift register into avoltage necessary for driving a pixel, an output buffer circuit, and thelike.

The output buffer circuit in this embodiment is a circuit for amplifyinga held voltage or converting impedance thereof and for applying it tothe display portion, and various circuits including an inverter as atypical component are conceivable.

The alternating operation of this embodiment will be described belowwith reference to FIG. 4 showing an example of signal voltage waveformof the input video signal 120 of this embodiment.

First, the input video signal 120 is converted by the A/D conversioncircuit 114 into a digital signal. Various corrections (liquid crystaldisplay γ correction or camera γ correction, correction in conformitywith demands by an observer, etc.) are performed by the correctingcircuit 108, so that the signal is converted into a signal suitable forliquid crystal panel display. FIG. 4 shows the signal waveform at thistime. In this embodiment, the video signal is divided into two signalswhich are outputted to separate signal lines. By this division, it ispossible to lower the frequency of the video signal.

In this embodiment, although an example in which the analog video signalis divided into two signals, is shown, the signal may be divided intomore than two signals in the present invention. If such a structure isadopted, it is possible to further lower the frequency of the videosignal.

The two signals outputted from the correcting circuit 108 to theseparate signal lines are converted into analog signals respectively bythe corresponding D/A conversion circuits 109 and 110.

The voltages of the two analog signals are amplified respectively byamplifiers of the corresponding reversal process circuits to makesignals having voltage values (about −5 V to about 5 V) suitable forpanel driving. At this point of time, both the two signal voltages arewithin the voltage value range of 0 to 5 V. That is, the two signalshave positive polarities with respect to the potential of the oppositeelectrode provided opposite to the pixel electrode as a center potential(reference potential). The polarity reversal signal 122 havingpolarities inverted every frame with the center potential as thereference is inputted to the two reversal process circuits as shown inFIG. 4. That is, in the two reversal process circuits, the video signalsare amplified and at the same time, on the basis of the inputtedpolarity reversal signal, the polarities of the video signals areinverted every frame, with the center potential as the reference.

In this embodiment, although the reversal period of a drive voltage ismade one frame period (one vertical scanning period), a period differentfrom this may be made a reversal period. For example, the reversalperiod may be made a two-frame period or a three-frame period.

Further, in this reversal process circuit, either one of the videosignals is inverted so that a pair of signals having symmetry areformed.

As shown in FIG. 4, the waveforms of the pair of signals have symmetrywith respect to the center potential, and become signal waveforms inwhich the polarities are inverted every screen. However, it is needlessto say that the sequence of signal processes in the reversal processcircuits 112 and 113 can be suitably changed by a circuit design.Moreover, as shown in FIG. 13 in which an example is shown, the sequencemay be modified such that a digital signal is subjected to a reversalprocess, and the signal is converted into an analog signal. By doing so,a digital signal is processed to the utmost degree, so that it ispossible to accurately process the signal. Like this, even in the signalprocessing circuit 106, it is possible to suitably change the sequenceof signal processes in a similar manner.

The two signals (shown in FIG. 4) in which the polarities are invertedevery screen and which have symmetry with reference to the potential ofthe opposite electrode provided opposite to the pixel electrode, areinputted to the source driver circuit 105.

Shift register portions of two phases are provided in the source drivercircuit 105. A first start pulse signal and a first clock signal areinputted to the first phase horizontal shift register, and the firstanalog video signal 129 sampled by the sampling circuit is outputted toan odd signal line. A second start pulse signal and a second clocksignal are inputted to the second phase horizontal shift register, andthe second analog video signal 130 sampled by the sampling circuit isoutputted to an even signal line.

In the case where the shift register portions of two phases areprovided, as compared with a case where a shift register of only oneline is used, the operation frequency of a shift register can be reducedto a half (½).

As an example of the present invention, a shift register of more thantwo phases may be used. For example, in the case where n-phase shifterregisters are used, as compared with the case where a shift register ofonly one line is used, the operation frequency of the shift register canbe reduced to 1/n.

Here, the operation of the respective pixels in the case where the videosignals of FIG. 4 (the first analog video signal 129, the second analogvideo signal 130) are applied, will be described with reference to FIG.2 showing an example of a circuit diagram of the vicinity of the sourcedriver circuit 105.

When a signal voltage (turning on a TFT provided in the vicinity of anintersecting portion) is applied to only a scanning line A, pixel TFTsare turned on, the first analog video signal 129 is applied to thesignal line (1) synchronously with a scanning signal, and a positivesignal is applied to a pixel electrode Al connected to the odd signalline (1).

Next, in the same manner, the second analog video signal 130 is appliedto the signal line (2) synchronously with a scanning signal, and anegative signal is applied to a pixel electrode A2 connected to the evensignal line (2).

By repeating these operations, positive signals are sequentially appliedto the pixel electrodes (A1, B1, C1, . . . and A3, B3, C3, . . .) andnegative signals are applied to the pixel electrodes (A2, B2, C2, . . .and A4, B4, C4, . . . ).

After one frame period, when a signal voltage (turning on a TFT providedin the vicinity of an intersecting portion) is again applied to thescanning line A, since the polarities of the written first analog videosignal 129 and the second analog video signal 130 are inverted as shownin FIG. 4, the polarity of a signal applied to a pixel electrode isinverted.

By repeating these operations, the amount of transmitting light iscontrolled in accordance with the video signal, and by the combinationwith other pixels, a picture is displayed on the entire of the liquidcrystal panel.

In this way, source line reversal drive is carried out. In thisembodiment, the alternating drive (source line reversal) can be carriedout by using the video signal in which the polarity is inverted onlyevery screen. That is, as compared with a conventional method in whichthe polarity is inverted every pixel or horizontal scanning period, aplurality of signals in which the number of polarity reversals in eachsignal is small (the polarity is inverted every screen) are used, andthe source line reversal drive is carried out.

That is, since the number of polarity reversals is small, a phase shiftor a noise is not easily produced, and consumed electric power can bereduced. Thus, as compared with the conventional method, it is possibleto make picture display which is excellent in both horizontal resolutionand vertical resolution and in which a flicker is not easily produced.

EMBODIMENT 2

In the embodiment 1, the reversal period of the video signal is made oneframe period, and the source line reversal drive is carried out. Thisembodiment shows an example in which although the structure of a deviceis the same as the embodiment 1, the reversal period of the video signalis made one horizontal period in the reversal process circuit, so thatdot reversal drive is carried out.

In this embodiment, although the reversal period of a drive voltage ismade one horizontal scanning line, a period different from this may bemade a reversal period. For example, a two-horizontal scanning period ora three-horizontal scanning period may be adopted.

The dot reversal is an alternating drive method having a merit that aflicker is least noticeable since the polarities of voltages of videosignals are inverted between adjacent pixels.

The feature of the dot reversal drive is that as shown in FIG. 12C, inone frame, the polarities of voltages of applied video signals areinverted between adjacent pixel electrodes in the vertical direction andthe horizontal direction, and in the next frame, the polarities of therespective pixels are inverted.

In the conventional method, in order to perform the dot reversal, it isnecessary to carry out polarity reversal every pixel. However, if thedevice structure similar to the embodiment 1 is used, and a plurality ofvideo signals in each of which the polarity is inverted every horizontalscanning period (which have reversal relationships with each other) areinputted to the panel, the dot reversal drive can be made.

That is, in this embodiment, as compared with the conventional method inwhich the polarity is inverted every pixel, the dot reversal drive iscarried out by using the video signal in which the number of polarityreversals is small (the polarity is inverted every horizontal scanningperiod), so that accurate alternating drive can be carried out, and thereliability of the panel can be improved.

Thus, in this embodiment, as compared with the embodiment 1, it ispossible to obtain display with less flicker, high quality, and highfineness. Moreover, similarly to the embodiment 1, as compared with theconventional method, the consumed power can be greatly reduced.

EMBODIMENT 3

Although the embodiments 1 and 2 show examples in which shift registersof two phases are used, in this embodiment, an applied example in whicha one-phase shift register is used will be described. FIG. 5A is aschematic view of the vicinity of a source driver circuit of thisembodiment.

In FIG. 5A, reference numeral 501 denotes a clock signal, 502 denotes astart pulse, 503 denotes a shift register, 529 denotes a first analogvideo signal, and 530 denotes a second analog video signal. By using thevideo signal (polarity reversal period is one frame or one horizontalscanning period) as shown in the embodiment 1 or 2, it is possible tomake the source line reversal or dot reversal drive even by the sourcedriver circuit of FIG. 5. By making such a structure, it is possible tomake integration of drive circuits.

EMBODIMENT 4

FIG. 6 is a view showing the outline of a projection type picturedisplay device (rear projector) using a three-plate type optical system.In the projector (main body 600) of this embodiment, projection lightprojected from a light source 601 is separated into three primary colorsof R, G, and B by an optical system 613, and light rays of therespective colors are guided by mirrors 614 to three TFT liquid crystalpanels 610 displaying pictures of the respective colors. Light raysmodulated by the respective TFT liquid crystal panels are synthesized byan optical system 616 and a color picture is projected on a screen 605.Reference numeral 615 denotes a polarizing plate.

When the input picture signals are supplied to the respective liquidcrystal panels by using the liquid crystal panel, the signal processingcircuit, and the control circuit of the present invention, it ispossible to form the pictures of the respective colors, by the liquidcrystal panels, with high quality and high resolution in which there isno cross talk, no mottling, no flicker, and no color blur. In addition,since the liquid crystal display γ correction or camera γ correction,correction suitable for human vision, correction in conformity ofdemands by an observer, and the like are performed by the correctingcircuit, it is possible to obtain a picture having excellent γcharacteristics.

Thus, by using this rear projector, a picture which is vivid and hashigh color reproducibility and high gradation, that is, a picture havingexcellent gradation expression can be displayed on a screen.

In the present invention, although the active matrix type panel is usedas the liquid crystal panel, another liquid crystal panel with adifferent kind may be used.

The present invention can be applied not only to a drive circuitintegration type liquid crystal display device, but also to a so-calledexternal type display device in which a drive circuit is formed on asubstrate different from a liquid crystal panel.

The structures of the circuits shown in the embodiment 1 to 4, forexample, the structures of the shift register circuit, the buffercircuit, the sampling circuit, the memory circuit, and the like aremerely an example, and it is needless to say that the structures can besuitably modified as long as similar functions can be obtained.

As described above, according to the alternating drive method and devicestructure of the present invention, the reversal period of a videosignal when source line reversal drive display is carried out is greatlyprolonged from a conventional one pixel writing period to one screenwriting period, so that the present invention has effects that theconsumed electric power of a signal processing circuit and a sourcedriver circuit are reduced, and the consumed electric power of a liquidcrystal display device can be reduced.

Similarly, even in the case where dot reversal drive display is carriedout, the reversal period of a video signal can be greatly prolonged froma conventional one pixel writing period to one horizontal scanningwriting period.

That is, when attention is paid to one video signal line, it is notnecessary to invert the polarity of the video signal in one horizontalscanning line period, so that electric power necessary for chargingcapacitance of the video signal line is small, and further, as comparedwith the conventional method, a change in potential is small, so that asignal deterioration or a phase shift is small, and accurate pictureinformation can be supplied to the respective pixels.

In addition, since the input video signal is divided into a plurality ofvideo signals having reversal relationships with each other, the periodof change of the video signal becomes long, and the frequency of thevideo signal can be reduced. Also in the source driver, it is possibleto reduce the frequency of a clock signal by using shift registers ofplural phases. Thus, since the frequency of the video signal having arelatively high frequency band region can be reduced, a sampling circuitand the like can be easily constituted by using TFTs, and it becomespossible to make display with high fineness constituted by video signalshaving a high frequency band region, which are conventionally difficultto be displayed.

According to the structure of the present invention, it is possible tomake picture display with high fineness and high quality, which isexcellent in horizontal resolution and vertical resolution and in whicha flicker is not easily generated. That is, it is possible to obtain apicture having high gradation, that is, a picture having excellentgradation display.

1. A projection type display device including at least a screen and apanel, the panel comprising: a pixel including a switching element,wherein the switching element is electrically connected to a scan lineand a signal line, a gate driver electrically connected to the scanline, a source driver electrically connected to the signal line, and asignal processing circuit for providing a first video signal and asecond video signal to the source driver.
 2. The projection type displaydevice according to claim 1, wherein the source driver includes asampling and a buffer circuit.
 3. The projection type display deviceaccording to claim 1, wherein the first video signal and the secondvideo signal have a reversal relation to each other.
 4. The projectiontype display device according to claim 1, wherein the first video signalis inputted to an odd signal line through a first video signal line, andwherein the second video signal is inputted to an even signal linethrough a second video signal line.
 5. The projection type displaydevice according to claim 1, further comprises a light source.
 6. Theprojection type display device according to claim 1, further comprisesan optical system.
 7. The projection type display device according toclaim 1, further comprises a mirror.
 8. A projection type display deviceincluding at least a screen and a panel, the panel comprising: a pixelincluding a switching element, wherein the switching element iselectrically connected to a scan line and a signal line, a gate driverelectrically connected to the scan line, a source driver electricallyconnected to the signal line, and a signal processing circuit forproviding a first video signal and a second video signal to the sourcedriver, wherein the source driver applies the first video signal to anodd signal line, and applies the second video signal to an even signalline.
 9. The projection type display device according to claim 8,wherein the source driver includes a sampling and a buffer circuit. 10.The projection type display device according to claim 8, wherein thefirst video signal and the second video signal have a reversal relationto each other.
 11. The projection type display device according to claim8, wherein the first video signal is inputted to an odd signal linethrough a first video signal line, and wherein the second video signalis inputted to an even signal line through a second video signal line.12. The projection type display device according to claim 8, furthercomprises a light source.
 13. The projection type display deviceaccording to claim 8, further comprises an optical system.
 14. Theprojection type display device according to claim 8, further comprises amirror.
 15. A projection type display device including at least a screenand a panel, the panel comprising: a pixel including a switchingelement, wherein the switching element is electrically connected to ascan line and a signal line, a gate driver electrically connected to thescan line, a source driver electrically connected to the signal line,and a signal processing circuit for providing a first video signal and asecond video signal to the source driver, wherein the source driverincludes a first shift register and a second shift register, wherein thefirst shift register is electrically connected to an odd signal line,and wherein the second shift register is electrically connected to aneven signal line.
 16. The projection type display device according toclaim 15, wherein the source driver includes a sampling and a buffercircuit.
 17. The projection type display device according to claim 15,wherein the first video signal and the second video signal have areversal relation to each other.
 18. The projection type display deviceaccording to claim 15, wherein the first video signal is inputted to anodd signal line through a first video signal line, and wherein thesecond video signal is inputted to an even signal line through a secondvideo signal line.
 19. The projection type display device according toclaim 15, further comprises a light source.
 20. The projection typedisplay device according to claim 15, further comprises an opticalsystem.
 21. The projection type display device according to claim 15,further comprises a mirror.